In Taï National Park in Ivory Coast, Oscar is a young chimpanzee in his toddler years and is part of a close-knit tribe of chimpanzees who occupy a forest territory which is rich in native fruits, nuts, and figs. The chimpanzees hunt small tree monkeys, and they also eat termites collected with primitive tools made from sticks. They also use rocks as tools to crack nuts. Oscar is tended by his mother, Isha, and from her he begins learning many things about how to survive in the jungle. In the chaos of an attack by a rival gang of chimpanzees led by Scar, Isha is injured and separated from the group and her son. As told by the narrator, Isha most probably falls victim to a nocturnal leopard.
Unaware of his mother's death, Oscar spends much of his time looking for her. He has trouble recalling the things she taught him and loses weight quickly. He attempts to find another mother to take care of him. However, none of the females in the group can afford to help him, already having young of their own to raise. As time goes on, Oscar is rejected by all the chimpanzees in the group, until the only one left to approach is the tough-skinned alpha male, Freddy. As Oscar follows Freddy and imitates him, it is soon revealed that this unlikely pairing may work out. The two gradually warm up to each other more and more, until one day Freddy lets Oscar ride on his back, something normally only mother chimpanzees do.